The present invention relates in general to an apparatus and process of making magnetically readable cards, and more particularly, to such an apparatus and process which prevents deformation or distortion of the thermoplastic carrier layer which supports the magnetic material and which forms a primary component of the magnetically readable cards.
Magnetically readable cards are frequently used as credit cards, bank cash machine cards, security passes and the like. These cards are typically constructed from a relatively heavy, rigid vinyl polymer core with thin vinyl polymer cover sheets or over-laminae bonded to opposite faces of the core. The core is often printed, whereas the cover sheets are transparent to allow readability of the printed material. The cover sheets are generally bonded to the core by application of both heat and pressure. To permit encoding of information on the card, the magnetically readable card includes a magnetic strip at or near the surface of the card. The magnetic strip incorporates a ferromagnetic powder such as an iron oxide in a binder including polymers such as vinyls. To provide satisfactory interaction with magnetic reading and writing equipment, the magnetic strip and the surrounding surfaces of the card should be precisely flat and free of defects. Moreover, the magnetic strip should be precisely flush with the adjacent surfaces of the card and should have a uniform thickness and straight edges. The magnetic strip also must be securely bonded to the remainder of the card.
Magnetic material ordinarily is formed into a thin layer on a carrier layer such as a polyester sheet by a solvent coating process. The carrier typically is a polyester-based polymer such as polyethylene terepthalate ("PET") which can withstand the solvents used in the coating process. The resulting laminate is ordinarily provided with a meltable release layer disposed between the magnetic layer and the carrier layer and a heat active adhesive directly overlying the magnetic layer. The laminate can be slit into continuous strips or tapes. The magnetic layer can be transferred from its carrier layer directly to the card by placing the strip or tape on the card so that the adhesive layer faces the card, and then, applying heat and pressure through the carrier layer to melt the release layer and activate the adhesive, thus bonding the magnetic layer to the card. The carrier layer ordinarily is stripped off of the magnetic layer at this point.
It has been widely believed in the art that the heat and pressure applied in such a transfer operation necessarily would lead to severe distortion or deformation of a vinyl polymer sheet as a result of substantial thermally caused shrinkage unless the sheet is relatively thick. In processes such as those disclosed in U.S. Pat. Nos. 4,149,925 and 4,231,828, the magnetic material is transferred from its carrier directly to individual cards by feeding each card with a strip of the laminate superimposed thereon through a nip defined by a heated roller and a reaction roller. The carrier sheet of the laminate contacts the heated roller, whereas the adhesive layer of the laminate contacts the card. Heat transferred through the carrier layer activates the adhesive layer and melts the release layer, so that the magnetic material separates from its carrier layer and bonds to the card. The card as fed into the nip typically must include a relatively stiff or rigid core, ordinarily at least about 0.020 inches thick, in order to withstand the heat and pressure without unacceptable distortion. Handling individual cards is a relatively slow and hence expensive process.
Another process utilized heretofore produces a plurality of magnetically readable cards in a single production cycle. In this process, the core stock is provided as a large sheet having printed regions corresponding to a multiplicity of cards arranged in a matrix of several rows and columns across the face of the sheet, with waste or "gutter" spaces between those regions corresponding to individual cards. Cover sheets or over-laminae are superposed on the core stock and attached thereto only at an edge thereof. A plurality of strips or tapes of the aforementioned laminate are unwound from individual reels and laid onto one cover sheet so that each strip or tape lies in registration with the individual printed card regions. The magnetic material in each strip or tape is "tacked" or bonded to the cover sheet by localized application of heat and pressure at only those locations corresponding to the waste or gutter spaces between the printed card regions on the sheet of core stock. The carrier layer of each strip or tape is removed, leaving the magnetic material loosely attached to the cover sheet. The entire composite is then placed between a pair of heated platens and subjected to heat and pressure, so as to bond the cover sheets to the core stock and fuse the magnetic material with the adjacent cover sheet. Following the lamination step, individual cards are severed from the sheet of core stock by die cutting. Although the preliminary "tacking" step typically causes some distortion of the over-lamina and/or the underlying core stock, and hence some unevenness of the resulting magnetic layer, any such distortion and unevenness are confined to the waste or "gutter" areas of the sheets. The distorted regions thus do not appear in the finished cards after the die cutting operation.
This fabrication technique requires relatively complex equipment and procedures. The tacking operation must be discontinuous, to limit distortion of the over-lamina to the waste areas of the sheet. Moreover, the discontinuous process of unwinding only a limited length of each strip or tape and laying same onto a subassembly of cover layers and sheet of core stock of limited length is slow and troublesome. The original sheet of core stock must necessarily include waste areas to provide locations for tacking. Therefore, this process results in waste of PG,5 materials. The composite, after the preliminary tacking step, is relatively fragile and poses considerable handling difficulties.
These disadvantages have been overcome, in part, by manufacturing magnetically readable cards in accordance with the apparatus and process disclosed in my co-pending U.S. Application Ser. No. 114,095, filed on Oct. 27, 1987.
In this regard, stripes of encodable magnetic material are applied in the fabrication of magnetically readable credit cards by incorporating the magnetic stripes in the cover sheet itself, as a secondary carrier, and laminating the resulting cover sheet to the sheet of core stock forming the credit card. The laminated credit card composite is then severed into individual cards. The magnetic strip bearing cover sheet is fabricated by feeding a continuous cover sheet without the magnetic stripes continuously through a nip formed between a heated roller juxtaposed with a reaction roller along with a plurality of continuous magnetic strips arranged in parallel rolls in registration with that portion of the credit card where they will ultimately be bonded. Each magnetic strip is provided as a laminate composite including a release layer, a magnetic layer, an adhesive layer, in that order, supported on a primary carrier layer. Heat and pressure applied within the nip releases the magnetic layer from the primary carrier and activates the adhesive layer to bond the magnetic layer of each strip to the original cover sheet, thus forming a plurality of parallel magnetic strips on the cover sheet itself.
The cover sheet may be formed from a variety of polymers, and typically vinyl polymers such as polyvinyl chloride. As the cover sheet is frequently very thin, on the order of less then about 0.010 inches, as well as being thermally sensitive, the cover sheet is subject to deformation, i.e., wrinkling, by the substantial shrinkage thereof as a result of being subjected to heat during the bonding operation. It has been found that vinyl polymer sheets utilized for the cover sheet can have a shrinkage amount of 30 to 40% when subjected to uncontrolled heat during the processing operation. In order to overcome this shrinkage problem, the previously known process required close control of a variety of parameters and processing conditions, for example, the thickness of the cover sheet, the polymer material being used, the roller temperatures, the contact times, tension applied to the cover sheet, the roller surface speeds and the like. These parameters and processing conditions were required to be maintained within close limits to suppress wrinkling or distortion of the cover sheet. The difficulty in maintaining and controlling these parameters and processing conditions have made the aforementioned known process difficult to maintain and requiring process operators having engineering abilities typically not employed in such manufacturing operations. The slightest deviation from any one of the above parameters or processing conditions, could result in the wrinkling or distortion of the cover sheet with the resulting material being unusable.
Accordingly, there is the need for improvements in the manufacture of magnetically readable cards.